README.md

AzureFunctions.TestFramework.CosmosDB

CosmosDB Trigger, Input, and Output binding support for the Azure Functions Test Framework.

Installation

dotnet add package AzureFunctions.TestFramework.CosmosDB

Supported bindings

Binding	Attribute	Description
[CosmosDBTrigger]	Trigger	Receives a batch of changed documents from the CosmosDB change feed
[CosmosDBInput]	Input	Reads documents from CosmosDB (point-read or query)
[CosmosDBOutput]	Output	Writes documents to CosmosDB — captured via FunctionInvocationResult

CosmosDB Trigger

Use InvokeCosmosDBAsync to simulate a CosmosDB change-feed trigger with a batch of changed documents.

Strongly-typed documents

var documents = new[]
{
    new TodoItem { Id = "1", Title = "Buy milk", IsComplete = false },
    new TodoItem { Id = "2", Title = "Write tests", IsComplete = true }
};

var result = await host.InvokeCosmosDBAsync("ProcessCosmosDocuments", documents);

Assert.True(result.Success);

Raw JSON

var json = """[{"id":"1","title":"Buy milk"},{"id":"2","title":"Write tests"}]""";

var result = await host.InvokeCosmosDBAsync("ProcessCosmosDocuments", json);

Assert.True(result.Success);

CosmosDB Input Binding

Register fake documents via the builder so they are injected automatically for every invocation:

var host = await new FunctionsTestHostBuilder()
    .WithFunctionsAssembly(typeof(MyFunction).Assembly)
    .WithHostBuilderFactory(Program.CreateHostBuilder)
    // Single document for [CosmosDBInput(databaseName: "MyDb", containerName: "Items")]
    .WithCosmosDBInputDocuments("MyDb", "Items",
        new TodoItem { Id = "1", Title = "Injected item", IsComplete = false })
    .BuildAndStartAsync();

Use WithCosmosDBInputDocuments<T>(databaseName, containerName, IReadOnlyList<T> documents) to inject a list of documents, and WithCosmosDBInputJson(databaseName, containerName, json) to inject raw JSON.

Function example

[Function("ReadCosmosItem")]
public void Run(
    [QueueTrigger("items-queue")] string queueMessage,
    [CosmosDBInput(databaseName: "MyDb", containerName: "Items", Id = "%itemId%")] TodoItem? item)
{
    if (item is not null)
        _logger.LogInformation("Read item: {Title}", item.Title);
}

CosmosDB Output Binding

Output bindings are captured automatically via FunctionInvocationResult:

var result = await host.InvokeCosmosDBAsync("CreateCosmosDocument", documents);

Assert.True(result.Success);
var written = result.ReadOutputAs<TodoItem>("outputDocument");
Assert.Equal("expected-id", written?.Id);

Function example

[Function("CreateCosmosDocument")]
[CosmosDBOutput(databaseName: "MyDb", containerName: "Items")]
public TodoItem? Run([CosmosDBTrigger(...)] IReadOnlyList<TodoItem> documents)
{
    return documents.FirstOrDefault();
}

Testing across all four flavours

Add the CosmosDB package reference to your test project and all four function-app test flavours:

<PackageReference Include="AzureFunctions.TestFramework.CosmosDB" />

See the 4-flavour matrix test pattern for the concrete test class structure.